the report wrote:after a near death experience
..
began walking exclusively on her hind legs after a stomach ailment nearly killed her, zookeepers said.
..
One possible explanation is brain damage from the illness, he said.
..
Otherwise, Horowitz said, Natasha's behavior has returned to normal.
I wonder if the stomach ailment left her uncomfortable, and standing upright relieves the discomfort.
If it's brain damage, then it's a bit surprising that all her other bahaviors have returned to normal.